This study will examine the mechanisms involved in the homo-regulation of intracellular pH in human colonic crypts and their relationship to altered colonic crypt cell proliferation. Epidemiological studies have shown that stool pH is elevated in populations with an increased prevalence of large bowel cancer. Furthermore, patients with colon cancer have a higher stool pH than control patients. Recent studies from our laboratory have shown that intramucosal pH is elevated in patients with colorectal cancer even in the absence of luminal substrate. Growth factors and mitogens that stimulate the phosphoinositol pathway result in increased cytoplasmic pH and Ca2+ activities. Because we and others have demonstrated activation of Na:H exchange during the induction of large bowel cancer in rodents and because the uncoupling of dual Na:H Cl:HCO3 transporters has recently been observed in this model, we propose to examine pH regulation in control and cancer-bearing human large bowel mucosa. Confocal microscopy and intracellular fluoroscent dyes (SNARF) will be used to map the cytoplasmic pH profile along the length of human colonic crypts and at different sites along the colon in relationship to a primary colorectal cancer. These results will be compared with normal colonic crypts obtained from organ donors. The regulation of pHc at different levels along the crypt and under variable conditions of extracellular pH, sodium, potassium, bicarbonate and chloride will be examined. Concurrent studies of crypt cell proliferation will be carried out using three dimensional native state cultures and measurement of thymidine uptake and itotic index. We will thus compare alterations in crypt cell pHc homeostasis with standard measurements of cell proliferation using native state three dimensional crypt cultures. These studies will allow us to understand the relationship of altered pHc homeostasis at the crypt and cellular level and how it relates to altered proliferation of cancer-adjacent, distant and control large bowel mucosa.